Security device and system

ABSTRACT

A security device ( 100 ) comprises at least one magnetic element ( 102 ). The magnetic element ( 102 ) is responsive to an applied magnetic field to provide a characteristic response. The characteristic response can be used to identify a particular security device ( 100 ) when interrogated by a security system, thereby aiding in prevention of copying of the security device ( 100 ).

The present invention relates to security devices and methods. Inparticular, the present invention relates to security devices andmethods for identifying unauthorised copying of goods etc. to which suchsecurity devices are applied.

As is known, and discussed herein, copying of various products such as,for example, documents, passports and goods etc., is a common problem.Counterfeiters and/or pirates often copy items having various levels ofcopy protection and have become increasingly adept at evading existinghigher level copy protection schemes. For example, they are increasinglycopying items such as credit cards by reproduction of magnetic strips,passports with holograms etc.

Various aspects and embodiments of the invention seek to provide a wayfor improving detection of copied items to reduce the effects ofcounterfeiting.

According to a first aspect of the invention, there is provided asecurity device comprising at least one magnetic element. The at leastone magnetic element is responsive to an applied magnetic field toprovide a characteristic response. This characteristic response isinherently difficult to reproduce as it depends upon uncontrollablenano-scale variations in the structure of the magnetic elements. Thus, askilled scientist, even one who understands the technology, cannot copysuch security devices using current technology, even if he wanted to.The inherent variability of such nano-scale variations may also providethat many such characteristic responses are obtained for individualsecurity devices, thereby ensuring that a brute-force approach toreproducing them requires an extremely large number of such devices tobe made before an acceptable copy can be made. (e.g. it may be necessaryto produce millions or billions of such devices before a suitable copyis made)

Security devices may be provided with an identifier to identify anindividual security device. Identifiers may be unique. Where uniqueidentifiers are provided, any attempt at brute force copying requires acopier to make an extremely large number of devices for each identifierbefore one acceptable copy can be made. Hence a copier cannot readilysimply stock a large number of devices and select ones with matchingcharacteristic responses unless he stocks a large number per identifier:e.g. where there is a 1 in 2×10⁶ chance of randomly copying a securitydevice and 2³² identifiers are provided, a forger has to produce2×10⁶×2³² identifiers to have an even chance of copying a singlesecurity device: this number is enormous: i.e. 8,589,934,592,000,000.Hence, the difficulty in copying a given device becomes apparent.

Identifiers may be formed by the magnetic elements themselves. Invarious embodiments a pattern of one or more of the identifiers may beused to define a unique identifier. Such magnetic elements provide boththe characteristic response and the unique identifier, making them evenmore difficult to copy as the characteristic response and the uniqueidentifier are both provided, inseparably, by the same physicalstructure(s).

According to another aspect of the invention, there is provided a methodof manufacturing a security device, comprising providing at least onemagnetic element, wherein the at least one magnetic element provides acharacteristic response in response to an applied magnetic field. Thecharacteristic response provided may be used to provide a premeasuredcharacteristic response that may subsequently be used in identificationof the security device that generated it.

According to another aspect of the invention, there is provided a systemfor reading a security device, comprising: a magnetic field generationsystem for applying a magnetic field to a security device; and adetection system for measuring one or more parameters representative ofa measured characteristic response of said security device in responseto said magnetic field, wherein said system is operable to compare saidone or more parameters representative of a measured characteristicresponse to one or more respective parameters of a premeasuredcharacteristic response to determine whether respective measured andpremeasured parameters are substantially equivalent.

According to another aspect of the invention, there is provided a methodfor reading a security device, comprising applying a magnetic field to asecurity device; measuring one or more parameters representative of ameasured characteristic response of said security device in response tosaid magnetic field; and comparing said one or more parametersrepresentative of a measured characteristic response to one or morerespective parameter(s) of a premeasured characteristic response todetermine whether respective measured and premeasured parameters aresubstantially equivalent.

Security devices can be incorporated into products etc. duringmanufacture and/or thereafter. They may be used to detect counterfeitgoods, products etc. by comparing the premeasured characteristicresponse with a measured characteristic response. Various premeasuredcharacteristic responses may be used to compare a premeasuredcharacteristic response with a measured characteristic response for asecurity device according to an identifier associated with that securitydevice.

Security devices can be incorporated into products such as, for example,one or more of: a document; a passport; an identity card; a compactdisc; a digital versatile disc; a software product; packaging; an itemof clothing; an item of footwear; a smart-card; a credit or bank card; acosmetic item; an engineering part; an accessory; and any other goodsand/or items of commerce, whether manufactured or otherwise. In orderthat counterfeit or forged variants thereof may be identified.

The term magnetic element is intended to include any element formed ofany material that provides a measurable signal in response to an appliedmagnetic field, whether or not that material itself possesses aninherent magnetisation.

One aspect of the invention relates to a security device, for example tocomprise an identification and/or authentication device for use inisolation or for use in association with, incorporated into or onto orattached to another article. The security device provides acharacteristic response or signature for identification and/orauthentication in a manner that limits or makes difficult the copying ofthe device, and consequently the copying or counterfeiting of any itemused in association therewith. Another aspect of the invention relatesto a data reader particularly suited to reading such a characteristicresponse/signature, to a method of producing/measuring such acharacteristic response/signature in a security system including deviceand reader, and/or to an identification or authentication method usingsuch a device and/or system.

A major loss of revenue to many businesses and a substantial source ofcriminal activity arises from illegal counterfeiting or copying ofitems. Examples include, but are not limited to:

-   -   Copying cards and like devices used for paperless financial        transactions such as credit card and bank cards to allow        unauthorised transactions and withdrawals from ATMs;    -   Forging and copying items used for identification, such as        passports, visa documents, driving licenses, personal identity        cards and the like;    -   Copying material carried on a data storage medium, such as CD        and DVD disks;    -   Forging and copying official documents such as certificates;    -   Duplicating smart cards used for identity/access purposes, for        example to control access to areas as part of a security system,        to control access to services such as pay-TV, to control or log        use of hardware such as computers or other office equipment in a        multiple user environment;    -   Copying security or authenticity labels as part of counterfeit        goods manufacture, to make unauthorised and/or inferior copies        of high-value branded goods, high specification safety-critical        goods and the like.

This is a particularly identified problem in relation to cards and likedevices used for paperless financial transactions and for identificationpurposes, and this area has led development of security systems, whichare nevertheless likely to be generally applicable to most or all areaswhere copying is a problem.

As paperless commercial and general security systems have become moresophisticated, increased automation coupled with an increasedinformation storage capacity on the item have created greatopportunities for financial and identity fraud by copying of suchdocuments. The concentration of wealth and/or information accessiblethrough credit and bank cards and identity documents has increased.There has developed a growing need for accurate verification andidentification such items and/or effective copy prevention.

Card and documentary systems in particular have adopted measures thatimprove security by making counterfeiting difficult or inconvenient.This approach has concentrated in particular on incorporation ofembedded devices on or in the card or other document which are difficultto copy effectively. Examples include holographic images, diffractiongratings, specialist substances (inks, materials etc), embossedstructures, structures within the material of the card, etc.

Ultimately though, these markings can be copied by the sophisticatedcounterfeiter, and will be if the rewards are sufficient. There exists ageneral desire for a security marking that cannot practically becounterfeited.

An effective strategy against unauthorised copying of items exists if arandom signature or characteristic response can be associated with theitem or with a device that is attached to the item. The randomsignature/characteristic response could come from some uncontrollablemanufacturing process that can never be duplicated precisely. Thus,there always exists some small difference between the original item andits copy; if this difference can be detected and compared with apreviously measured response (e.g. a baseline response in which theresponse of individual magnetic elements are recorded separately, or theaverage response of a collection of such magnetic elements are recorded)taken from the original item, forgery can be identified.

There are 4 primary preferred requirements of a practical randomsignature:

-   -   That it be possible to measure the signature easily and without        excessive cost;    -   That it be possible to represent the baseline signature easily,        preferably by a small list of digital numbers.    -   That there be a large degree of randomness inherent in the        manufacture of the signature, such that every signature is        slightly different;    -   That it not be possible to control the manufacture of the        signature so that its randomness could be stripped out or        suppressed and an identical copy of an existing signature made.

Difficulties in achieving all of these requirements have to date limitedthe practical applicability of the concept on a wide scale in everydaysystems.

Viewed from a first perspective the invention provides a security devicefor an item which is inherently difficult to copy and thus limitscounterfeiting.

Viewed from another perspective the invention provides a security devicefor an item based upon a random signature which is readily manufacturedand measurable on a scale and at a cost appropriate for everyday use inauthentication/counterfeit prevention of high value items.

Viewed from a further perspective the invention provides a data readerparticularly suited to reading the signature of such a device.

Thus, according to the invention in a first aspect there is provided asecurity device comprising at least one and preferably a plurality andmore preferably a large plurality of magnetic elements arrayed on asuitable substrate and having a machine readable magnetic signatureresponse, provided in combination with a predetermined baseline magneticsignature response reading.

In various embodiments, the magnetic elements may comprise thin layermagnetic material, such as thin magnetic wires. The magnetic materialmay comprise macroscopic wires and/or dots, microscopic wires and/ordots and/or nanowires and/or nanodots, laid down in suitable form on asuitable substrate to give a machine readable magnetic marking, with ameasurable baseline signature signal highly dependent upon the preciseinherent structure. The predetermined recorded baseline signatureresponse gives a comparative figure, an “expected” response which can beused in connection with a measured response to authenticate the device.

As used herein, “device” at its broadest comprises the magneticelement(s) as hereinbefore described to be laid down on a suitablesubstrate, such as, for example, the surface of an item to which asecurity device is to be applied. Examples of the application of such adevice include without limitation such a device constituting orcomprising a part of an object adapted for use in its own right as anidentification, authentication, key or any other application; a deviceconstituting or comprising part of such an object provided for use witha second object, in particular for example as an attachment thereto, forauthentication, identification or other labelling, related security orother purposes; a device portion incorporated into or onto a second itemfor such identification, authentication or related security or otherpurposes. In particular, the device is provided to authenticate andimpede/prevent unauthorised counterfeiting by copying or cloning of anarticle of which it forms a part, or with which it is associated.

Examples of suitable collections of magnetic elements are described inR. P. Cowburn, Journal of Physics D, 33, R1 (2000). The presentinvention may rely upon their singular effectiveness in creating arandom signature for anti-forgery.

The magnetic elements are such that when a time-varying magnetic fieldis applied to the elements, their magnetic response is a non-linear andhysteretic function of that applied field. This non-linearity may becharacterised by discrete jumps in the magnetisation at certain appliedfield values. The elements are such that the small differences infabrication which must naturally exist from one element to another willcause the magnetic response to vary slightly from element to element.Furthermore, for various embodiments, the elements are such that a givenelement responds in as similar a way as possible to each cycle of thetime-varying applied magnetic field.

In order to determine the baseline signature response of a collection ofmagnetic elements, a time-varying magnetic field is applied to theelements, and the magnetic response of the elements is recorded. Theresponse can be measured using the device described herein, or by someother means.

The baseline response may be condensed by identifying specific features,such as sudden jumps, or the mean and standard deviation of theswitching fields. Alternatively, the baseline response may be convertedfrom a time-domain sequence of magnetisation measurements to afrequency-domain list of measurements. Alternatively, the baselineresponse may be unprocessed.

Measuring the predetermined baseline response is analogous to acalibration procedure. It is anticipated that the predetermined baselineresponse will only be measured once, at the time of manufacture and thatthe device will then be supplied to the user with the predeterminedbaseline response stored in a manner accessible to the user, for exampleremotely from the device, or in association with the device in a forminaccessible without authorisation. In particular, it is desirable thatthe predetermined baseline response is securely encrypted, especially ifheld on or with the device. Preferably the predetermined baselinesignature response is encrypted using an asymmetric encryption algorithmwith the private key used for enciphering being kept secret and thepublic key used for deciphering being made available to any reader ofthe device such that the expected predetermined baseline signatureresponse can be decrypted and comparison can be made with a measuredresponse.

In order to test the authenticity of an item protected by a randomsignature, it is necessary in various embodiments to apply atime-varying magnetic field to the magnetic elements and to record themeasured magnetic signature response of the elements to that appliedfield. The same procedure is used first to determine the predetermined,expected baseline response which is then stored as above, and then byuse of a suitable reader to obtain subsequently measured baselineresponses which can be compared to the predetermined, expected baselineresponse to authenticate the device.

Authentication relies on the inherently random nature of the device.Artificially fabricated magnetic elements make a very good practicalrandom signature because the magnetic switching field of each elementdepends critically upon the physical structure of the ends of theelements. Structural variations of only a few nanometres in size cancause significant changes to the switching field (K. J. Kirk, J. N.Chapman, and C. D. W. Wilkinson, J. Appl. Phys. 85, 5237 (1999)).Therefore, in order to replicate the random signature, it is necessaryto replicate the precise shape of the elements to near-atomic precision.This is unfeasible using current technology and is likely to remain sofor many decades. While near-atomic level manipulation is required tocopy the device described in this invention, a macroscopic measurementis sufficient to check authenticity, because when the structureundergoes magnetic switching, the entire structure switches together,making the magnetic response very easy to measure. Thus, the randomsignature according to this invention requires low-cost, simpleprocesses to interrogate it, but unfeasibly difficult engineering tocopy it. This is ideal for a practical random signature.

If the magnetic response of a collection of elements is recordedtogether as an ensemble measurement, it must be appreciated that thestatistical fluctuations upon which this invention is based will beattenuated. The attenuation factor will be 1/√{square root over (N)},where N is the number of nominally identical elements in the ensemble.Thus, if a collection of individual elements has a switching field witha standard deviation of 10 Oe, then a collection of ensembles of 100elements will only have a standard deviation of 1 Oe. The measurement ofthe magnetic response must therefore be made more carefully. On theother hand, the total volume of magnetic material has increased by afactor N, which makes the measurement easier to make.

In various embodiments, authentication relies upon a match between themeasured baseline response of the device, and a predetermined baselineresponse stored securely, in particular in encrypted form. A forgerattempting to forge a device incorporating a prerecorded baselineresponse in an encrypted form will be extremely unlikely to produce aperfect forgery having a measurable magnetic signature response matchingan encrypted prerecorded original. In the genuine device, thepredetermined baseline response is recorded in an encryption known onlyto the manufacturing company or those authorised thereby. If theprospective forger merely attempts to copy both the signature device andthe encrypt derived therefrom the forgery will fail, because even if theencrypt is copied exactly the magnetic signature response of the copieddevice will differ from the original. Thus, on the forgery, the measuredand predetermined and recorded signature responses will not match. Ifthe forger creates a copy of the signature device, he could insteadmeasure the baseline response of the forged device readily. However, hecould not create a suitable valid encrypt corresponding to the forgedbaseline response because he does not know the encryption. Thus, bothpossible copying strategies fail.

Thus, in accordance with various aspects of the invention, a practicalmethod of generating and reading a random signature using artificiallystructured magnetic materials is described which is for practicalpurposes nearly impossible to copy, and which thus offers a securitydevice which can authenticate originals and prevent counterfeiting bycopying of such originals.

The magnetic elements of various embodiments comprise thin layers ofmagnetic material, preferably less than 1 μm thick, and more preferablyless than 100 nm thick. They may be 10 nm thick or less, but bypreference will be generally around 40 nm thick.

The elements may all be nominally identical in shape and of regularlydistributed arrangement, or differences between them and/or irregularpatterns of arrangement may have been intentionally introduced. Itshould be emphasised that the random nature of the magnetic response isan inherent consequence of material fabrication, not dependent upon theshape, configuration and distribution pattern of the elements.

The elements may be generally rectangular in shape, in particularelongate rectangular for example comprising an array of generallyparallel magnetic elongate rectangular elements, or may comprise areasof magnetic material, for example being square or circular, or someother regular geometric shape, which may for example be formed into atwo dimensional array.

As used herein reference made to magnetic wires, microwires or nanowiresshould be construed as being to such elements of elongated form, and inparticular elongate rectangular elements and/or elongate elements in agenerally parallel array, but not restricted to the parallel rectangularexamples given herein for illustration purposes. As used hereinreference made to magnetic dots, microdots or nanodots should beconstrued as being to such elements comprising areas of magneticmaterial of less elongate, more squat form, and in particular of regulargeometric shape, and/or formed into a two dimensional array, but notrestricted to the circular geometry of the examples given herein forillustration purposes.

The elements may be discrete, with no magnetic material connecting them,or they may be partially connected by magnetic material into a number ofnetworks, or they may be entirely connected by magnetic material into asingle network.

The elements may be made from a magnetic material, which will bypreference be magnetically soft, for example based on nickel, iron,cobalt and alloys thereof with each other or silicon, such as nickeliron alloy, cobalt iron alloy, iron silicon alloy or cobalt siliconalloy.

The elements may be coated with a protective overlayer to preventoxidation or mechanical damage, said protective over layer comprising athin layer of non-magnetic material having suitable mechanical and/orenvironmentally-resistant properties and/or surface treatments and/orcoatings, for example comprising a layer of ceramic, glass or plasticsmaterial. Such overlayers are conveniently transparent. Particularexamples of protective overlayers include titanium dioxide, transparentepoxy resin, plastic or glass, transparent modified silicone resinconformal coating and transparent acrylic conformal coating.

The elements are laid down upon a suitable substrate. An underlayer mayexist between the elements and the substrate. The device may beincorporated directly into or upon the item which is to be protected, inwhich case the substrate may be the item which is to be protectedagainst forgery itself or some suitable substrate material laid downthereupon or incorporated therein for the purpose. Alternatively, thedevice may be incorporated into a separate unit such as a tag, label,certification etc, attachable to or otherwise useable in conjunctionwith an item to be protected, the attachable unit comprising orincorporating some suitable substrate material. Suitable substratematerials include silicon, glass, plastic or some other material with asmooth surface.

In the case of the magnetic elements being formed on an attachable unit,the attachable unit may be attached directly to the item to beprotected, or may form part of a certificate or other documentationassociated with the item to be protected. Means may be provided inassociation with an attachable unit to effect attachment between theunit comprising an identification device in accordance with theinvention and the item to be protected. Such means may provide forreleasable, removable engagement of the attachable unit to the protecteditem, or for permanent engagement thereupon. In the former case,attachment means may further comprise locking means to ensure that onlyauthorised persons can remove the unit. In either case, the attachmentmeans may further comprise anti-tamper protection and/or mechanisms toindicate tampering by unauthorised persons.

Suitable uses for such attachable unit include, without limitation,labels for items of value, of security importance, or of otherwisecritical importance, for example to enable identification of thearticle, authentication of the article as genuine, verification of theprovenance of the article and the like and/or to label the article in asecure and controlled manner, for example with information about thearticle, pricing information, stock control information etc.

In the case of magnetic elements being formed directly upon an item tobe protected, similar usages might also be envisaged. Such directincorporation of the device onto the item to be protected however willbe singularly effective in preventing unauthorised reproduction, giventhe random and hence inherently non-controllably reproducible nature ofthe signature device, and will therefore be particularly useful inassociation with items which might be susceptible to the production ofcounterfeit copies, since the device will provide for readyauthentication of an item as original.

The elements may be formed by optical lithography, for example, usingthe method described herein, although embossing or some other form ofcontact printing may be used.

The plurality of elements making up the device may be of generally thesame size and shape, or may have a size and/or shape differingcontinuously or discontinuously across the device. Preferably, a numberof different element sizes will be present in one ensemble.

In one embodiment, several discrete groups of differently sized and/orshaped elements, the elements being generally similarly sized or shapedwithin each group, are provided so that several different switchingfields can be identified. For example, an ensemble of rectangularelements in parallel array may comprise several discrete groups ofdifferent widths.

A suitable example comprises 100 rectangular elements, each 1 mm long;10 will be 5.0 μm in width, 20 will be 2.5 μm in width, 30 will be 1.7μm in width, 40 will be 1.2 μm in width. The magnetic response of suchan ensemble will then show four distinct groups of switching fields,each of which will exhibit a statistical variation from one tag to thenext, which can be used to form a random signature.

A second example comprises 450 rectangular elements, each 1 mm long; 150will be 1.0 μm in width, 120 will be 1.25 μm in width, 90 will be 1.67μm in width, 60 will be 2.5 μm in width and 30 will be 5 μm in width.The magnetic response of such an ensemble will then show five distinctgroups of switching fields.

In the examples, the number of elements in each group is such that eachgroup should cover generally the same area. The strength of the detectedsignal from the reader usually depends upon the total area of coverage,so each of the four or five groups of switching fields will register thesame strength at the reader. This is a preferred feature for manyapplications, but it can be envisaged that for other applicationsseveral discrete groups of differently sized and/or shaped elements maybe provided wherein different groups occupy different areas of thedevice.

In an alternative embodiment, differently sized and/or shaped elementsare provided in a continuously varying array, so that variations in sizeand/or shape between an element and its neighbours are minimised toavoid large discontinuities. For example the area of an element shouldvary from its neighbours by no more than 5% and in particular by about1%. As a result, a smoothly varying collection of switching fields isproduced. The variation could be tuned in accordance with a suitablefunctional form which may be linear or non-linear.

For example, in an analogous device to that described above withrectangular elements in parallel array the width of the elements variesas a smooth function across the array. An ensemble might start with a2.5 μm wide wire; the next would be 2.53 μm, the next 2.56 μm etc, until56 wires later the width has risen to 5 μm. The total wire width is 200μm in this example. An alternative ensemble might start with a 1 μm widewire; the next would be 1.01 μm, the next 1.02 μm etc, until 450 wireslater the width has risen to 5 μm. Different functional forms, e.g.linear, quadratic etc could be used to determine the progression ofwidths across the ensemble. Unlike the previous example, this would notgive distinct groups of switching fields, but rather a smooth collectionof switching fields.

In one embodiment, the device, in addition to the signature arraycomprising a large plurality of signature elements, comprises a singlerelatively large area magnetic element for use as a reference element,for example a relatively wide magnetic nanowire or wide microwire. Inthe foregoing examples such a single wide wire could be 1 mm long and150 μm wide. For a wire at such a large width, the magnetic property isalmost identical to the bulk material, which is usually quite welldefined. Thus, in addition to five blocks which have erratic switchingfields there is provided one well defined switching field, which can beused to calibrate the reader. This calibration could include makingenvironmentally-based adjustments, such as subtracting the influence ofthe Earth's magnetic field, for example, or compensating for changes intemperature.

It is necessary that a predetermined base line magnetic signatureresponse is provided in combination with a security device in accordancewith various of the embodiments of the invention. It will however beunderstood that it is not necessary that such a predetermined base linemagnetic signature response is provided in physical association with thesecurity device, but merely that it is available to the authorised userof the device for comparison purposes to give an “expected” response tobe compared with an actual response when the device is read by suitablemeans, such as the magnetic signature reading means described herein.

Various embodiments may be provided. In a first, the pre-recordedbaseline may be provided in physical association with the device orprotected item. In a second, the pre-recorded baseline may be stored bya device reader. In a third, the pre-recorded baseline may be remotelystored from both device and device reader in a manner accessible to anauthorised person such that the necessary comparison between expected(i.e. pre-recorded) and actual (measured) baseline readings can be madefor authentication purposes.

In the first embodiment mentioned above, the pre-recorded baselineresponse is provided in close physical association with the device orprotected item. In one alternative, the pre-recorded baseline is storedin physical proximity to the device in machine-readable form. Forexample, the pre-recorded baseline is stored as a part of the device; oris stored adjacent to or under the device on a common substrate; or isstored in the vicinity of the device as part of a unit incorporating thesecurity device of the invention, optionally with other security orinformation features, such as a smart card, identification document, keycard, key fob or the like, or a label for an article to be protected; oris stored on or with an article to be protected which article to beprotected has also been provided with a device in accordance with theinvention; or is stored as part of a certificate or other documentationassociated with an item to be protected which certificate or otherdocumentation may also incorporate such a device in accordance withvarious embodiments of the invention.

In this embodiment, the prerecorded baseline should be stored inreadable but encrypted form. For example, the condensed or unprocessedbaseline response is digitally signed using an asymmetric encryptionalgorithm such as RSA. The private key, which is used for enciphering,is known only to the manufacturing company; the public key, which isused for deciphering, is held on every reader terminal which might beused to read the device.

The digitally signed and encrypted baseline response is stored on theitem, preferably with the magnetic elements for example in that it isprinted underneath or alongside the elements, or alternatively byrecording it onto a magnetic data strip, or by recording it onto anoptical bar code or by recording it onto a smart card chip, or by someother means. Other information, such as, but not limited to, the owner'sname or a unique identity code or a checksum may also be encrypted intothe same data stream and digital signature to prevent the magneticelements from being transferred to another item or important informationon a document or certificate from being modified.

1h the second embodiment referred to above, the prerecorded/premeasuredbase line response is stored on, by or in close association with adevice reader. Such an embodiment lends itself in particular to “lockand key” type systems where the device acts as a key and is used inassociation with a reader acting as a lock to limit access to particularareas, operation of particular items, or use of particular services tothe specified key holder(s).

in this embodiment, it is not necessary for prerecorded baselinesignature data to be stored upon or in close association with the deviceitself or a protected item. Optionally however, the data may still bestored in an encrypted form for security, for example in the mannerabove described, or may be otherwise security protected.

In the third embodiment referred to above, the prerecorded/premeasuredbaseline signature data is stored remotely from both the device andprotected item and the device reader. Such a mode of operation lendsitself in particular to, but is not limited to, systems where a networkcomprising a large number of readers each expecting to interrogate alarge number of devices is envisaged, for example as might be the casewith credit cards and the like with multiple points of sale, securityand identification systems with multiple points of access etc.

In accordance with this embodiment prerecorded signature data about thedevice, and in particular about a plurality of different devices, ispreferably stored at a central data store, for example connected to aplurality of readers on a distributed network. In such a network twoalternative modes of operation can be envisaged. In the first, a readeris adapted to read a device, interrogate a central data store for theprerecorded signature data, and make the comparison. In a second, thedevice reader is adapted to read the device and pass the actualsignature data to such a central data store for verification purposes.The essential principles remain the same.

In a further aspect of the invention there is provided a security systemincluding at least one device as hereinbefore described and at least onedevice reader, said device reader comprising means to read the magneticresponse of the device. In particular, the device reader comprises or isprovided in association with a magnetic field generator to apply atime-varying magnetic field to the elements, and has a magnetic responserecorder to record the response of the magnetic element to that appliedmagnetic field. An embodiment of a device reader is described herein.

For different applications, suitable systems may comprise a plurality ofsuch readers and/or a plurality of such devices. A system comprising aplurality of such readers may be arranged such that each readerfunctions independently in isolation, or such that some or all of thereaders are linked on a distributed network.

Readers provided for a system operated in accordance with the first modeof operation outlined above preferably further comprise means to readthe pre-recorded predetermined baseline signature response, inparticular the pre-recorded and encrypted signature response, stored on,with or in association with a device or protected article; andpreferably further comprise comparator means to compare the prerecordedand measured baseline signature responses. Readers adapted for a systemfor use in accordance with the second mode of operation described abovepreferably further comprise storage means for storing the predeterminedbaseline signature response(s) of the device(s) intended for usetherewith, and preferably further comprise comparator means to make acomparison between stored and measured baseline responses. Readersintended for use in accordance with the third mode of operationdescribed above preferably comprise means to receive data concerning aremotely stored predetermined baseline signature response, for examplevia direct entry of data by a user, or via interrogation of a remotedatabase on a distributed network, together with comparator means tocompare the predetermined response to the measured response; or in onealternative, means to transmit the measured response to a remotecomparator, which comparator incorporates or is in data communicationwith a store of predetermined responses.

In all cases, the device reader preferably makes a comparison betweenthe measured and predetermined baseline magnetic signature responses,for example against a predetermined tolerance limit, and actuates aresponse mechanism depending upon whether signatures are identical, forexample within those tolerance limits.

The response mechanism may comprise a simple display means, of anysuitable form, including visual, audio, alphanumeric indicators and thelike, of whether the device is authenticated. Additionally oralternatively, other responses may be provided for. For example,authentication might serve to release a real or virtual lock, permittingaccess to a restricted area, operation of an item of restrictedequipment, access to a particular service or the like.

According to a further aspect of the invention, a simple device isdescribed which can measure the magnetic response of a small area ofthin-film magnetic material. The device is well suited, but not limited,to measuring the magnetic random signature of a device such as describedabove. The small area will by preference be of size 0.2 mm×0.2 mm orgreater; the magnetic material will be in the thickness range 1 nm to500 nm, and by preference will be in the range 1 nm to 50 nm. Themagnetic material may be a continuous film or may be a collection ofmagnetic elements. The magnetic material may have a transparentprotective overlayer. In various embodiments the magnetic materialremains optically reflective.

In various embodiments according to this aspect of the invention adevice for measurement of the magnetic response of such an area ofmagnetic material as a time-varying magnetic field is applied to themagnetic material comprises an illumination source, and in particular aninfra-red illumination source; a collimator to focus the illuminationonto the surface of the magnetic material; and a collector to collectreflected illumination, and to monitor the varying response of thisreflection over time as the time-varying magnetic field is applied.Optionally, the device incorporates or is provided with a magnetic fieldgenerator to generate such a field.

In various embodiments, the transverse magneto-optical Kerr effect isused to measure the magnetic response of the area of magnetic materialas a time-varying magnetic field is applied to the magnetic material.This effect is well known in the literature. The response measuringdevice may incorporate additional means to apply such a time varyingmagnetic field to the area of magnetic material under investigation, ora separate device may be used to apply the same.

In various embodiments the device operates without polarised light.Conventionally, the transverse Kerr effect requires the incoming lightto be plane polarised. This is usually achieved by inserting a sheet ofPolaroid or some other polarising optical element in the in-coming beampath. It has been surprisingly found that in application to thisinvention, the polariser can be removed to reduce manufacturing cost andto reduce the size of the device. In the preferred embodiment of thepresent device a polariser is absent. This is suitable for manyapplications. Nevertheless it will be understood that a polariser may beincluded, for example in the in-coming beam path in conventional manner,where this is desirable or necessary.

Preferably, the collimator comprises a pinhole. At the scale of deviceoperation this is found to effectively focus the light without the needto use a lens. This again reduces manufacturing cost and reduces thesize of the device. Conveniently, the pinhole has diameter in the sizerange 0.2 mm-5 mm.

The light is then reflected off the surface of the magnetic thin film.Preferably, a second pin-hole, with diameter in the size range 0.2 mm-5mm, is provided to focus the reflected light. It is preferred that thesecond pin-hole should have the same diameter as the first pin-hole.Light is passed to a collector comprising a light sensitive device,which is by preference a phototransistor or photodiode sensitive to theradiation produced by the light source.

In various embodiments, the light source comprises a light emittingdiode. This is in contrast to prior art large scale devices formeasuring the magneto-optical Kerr effect where a laser or a dischargelamp or an incandescent lamp is used. The present device is smaller,cheaper and removes the hazards associated with a product containing alaser.

An infra-red light emitting diode (LED) is preferred over a visiblespectrum LED for two reasons: high optical intensities are achievable inthe infra-red due to the higher currents that infra-red LEDs cansustain; the optical receiver can be rendered insensitive to visiblelight, thus reducing interference from ambient light.

In various embodiments, the light source comprises a laser diode. Laserdiodes are relatively inexpensive and can provide high intensity light.

In a further aspect of the invention, a method of manufacture of asecurity device comprises forming at least one, and preferably a largeplurality of, magnetic elements as above described; obtaining a baselinesignature magnetic response for the elements; storing the baselineresponse as a predetermined baseline response in a form accessible to auser of the device, optionally by encrypting and storing in physicalassociation with the device in any readable form.

In various embodiments the elements will be formed by opticallithography.

In various implementations according to this aspect of the invention, acost saving can be made in the lithography process in the case of themagnetic elements comprising an array of generally rectangularstructures. The photoresist is applied to the substrate in the usualfashion and patterned by an optical exposure followed by development.The magnetic material is then deposited onto the patterned photoresist.Usually, the photoresist would then be dissolved in a solvent (lift-offprocess). However, the photoresist can be left in place, because themagnetic material deposited on top of it forms a second set ofrectangular magnetic elements. For example, suppose that the resist hadbeen patterned into rectangular structures of width 0.5 μM with acentre-to-centre spacing of 1.5 μm. If the photoresist is left in place,then the structures comprise a set of 0.5 μm wires attached to thesubstrate, and an equal number (minus 1) of 1 μm wires attached to thetop of the substrate.

The invention in a further aspect comprises a method of marking an itemfor security, identification or authentication purposes by use of theforegoing device and/or system and/or method and in particular byassociating a device as hereinbefore described therewith.

The invention in a further aspect comprises a method of identifying orauthenticating an item by use of the foregoing device and/or systemand/or method and in particular by associating a device as hereinbeforedescribed therewith, applying a time-varying magnetic field to theelements thereof to obtain a measured baseline magnetic signatureresponse, for example using the reader hereinbefore described, andcomparing the measured response to a predetermined recorded baselinemagnetic signature response.

Embodiments of the invention will now be described, by way of exampleonly, with reference to the appended figures in which:

FIGS. 1 to 4 show embodiments of security devices according to thepresent invention in perspective view;

FIG. 5 shows a further embodiment of a security device according to thepresent invention in plan view;

FIG. 5 a shows a another embodiment of a security device according tothe present invention in plan view;

FIG. 6 shows another embodiment of a security device according to thepresent invention shown in cross-sectional view;

FIGS. 7 a to 7 d illustrate magnetic switching modes of magneticelements that may be used in various embodiments of the presentinvention;

FIGS. 8 a and 8 b show idealised, schematic real and averaged hysteresiscurves for the magnetic switching of a permalloy material that may beused in various embodiments of the present invention;

FIGS. 9 a to 9 h illustrate a manufacturing technique for producingvarious embodiments of security devices according to the presentinvention;

FIG. 10 shows a reading arrangement forming a part of a security readingdevice system according to various embodiments of the invention;

FIG. 11 shows a mirror actuator for use in a security device readingsystem according to various embodiments of the invention;

FIG. 12 shows a further part forming a part of a security device readingsystem according to various embodiments of the invention;

FIG. 13 shows a signal that drives a magnetic field generator accordingto various embodiments of the invention;

FIG. 14 shows a signal that drives the mirror actuator according tovarious embodiments of the invention;

FIG. 15 shows one cycle of the signal of FIG. 13;

FIG. 16 shows a unipolar detector signal representing a characteristicresponse according to various embodiments of the invention;

FIG. 17 shows a synchronisation signal for synchronising varioussecurity device reading systems according to various embodiments of theinvention;

FIG. 18 is an illustration of a first collection of magnetic elementsused for a random magnetic signature/characteristic response inaccordance with the invention;

FIG. 19 is an illustration of a second collection of magnetic elements;

FIG. 20 is an illustration of a third collection of magnetic elements;

FIG. 21 is an illustration of a device for measuring the magneticresponse of a small area of thin magnetic film;

FIG. 22 is an illustration of an embodiment of the invention in a smartcard;

FIG. 23 is an illustration of an embodiment of the invention in anelectronic key;

FIG. 24 is an illustration of an embodiment of the invention in anidentity tag for attachment to an item to be protected;

FIG. 25 is an illustration of an embodiment of the inventionincorporated into a CD/DVD for authentication purposes; and

FIG. 26 is an illustration of an embodiment of the inventionincorporated onto a certificate for authentication purposes.

In various embodiments, magnetic materials are used to form magneticelements responsive to an applied magnetic field. The characteristicresponse of these magnetic elements to the applied magnetic field givesrise to a measurable characteristic response or signature foridentifying a security device including a set of such magnetic elements.

Many types of magnetic material are available that could be used to formmagnetic elements in various two-dimensional and three-dimensionalshapes: for example, magnetic wires, flattened wires, bars, dots, randomspots, random blobs etc. While many such materials can be used inembodiments of the invention, certain materials give a better magneticresponse than others when subject to an applied magnetic field;particularly if the magnetic switching properties of the material are tobe used as the, or as part of the, measurable characteristic response.

Where embodiments of the invention use the magnetic switching propertiesof the material to produce a characteristic response, magnetically softmaterials are useful. Magnetically soft materials are ferromagneticmaterials in which the magnetisation can be easily reversed. Thesematerials generally have narrow square-shaped hysteresis loops. Thus,the magnetisation of a magnetic element made from such a materialswitches its direction in response to an applied field relativelysharply. The coercivity of such materials (i.e. the reverse field neededto drive the magnetisation of a magnetic element made of such a materialto zero after being saturated) tends to be relatively low, therebyensuring that relatively low-field-strength magnets can be used to causea switch in the magnetisation direction of the magnetic element. Such,relatively low field-strength magnets may be fairly inexpensive,generally compact and easily driven to produce a controlled magneticfield of good uniformity.

FIG. 1 shows a security device 100. The security device 100 comprises aplurality of magnetic elements 102 formed upon a silicon substrate 104.The magnetic elements 102 are made of permalloy material.

FIG. 2 shows a security device 200. The security device 200 comprises aplurality of magnetic elements 202 formed upon a silicon substrate 204.The magnetic elements 202 are made of permalloy material. Data area 206is provided in the substrate 204 for storing encrypted premeasuredcharacteristic response information and/or a unique identifier foridentifying the security device 200.

The data area 206 of this embodiment comprises a set of etched pits (notshown) encoding binary data corresponding to encrypted premeasuredcharacteristic response information and/or a unique identifier that canbe read, for example, by an optical reader (not shown) in a manneranalogous to a compact disc.

In further variants of this embodiment, the data area 206 mayalternatively, or additionally, comprise electronic circuitry (notshown) that retains characteristic response and/or a unique identifierinformation.

FIG. 3 shows a security device 300. The security device 300 comprises aplurality of magnetic elements 302 formed upon a silicon substrate 304.The magnetic elements 302 are made of permalloy material. Data area 306is provided in the substrate 304 for storing encrypted premeasuredcharacteristic response information and/or a unique identifier foridentifying the security device 300.

In the data area 306 of this embodiment indicia 308 are provided. Theindicia 308 encode data corresponding to encrypted premeasuredcharacteristic response information and/or a unique identifier that canbe read by a reader (not shown). In one variant of this embodiment,visible indicia 308 are provided by a machine readable bar code (notshown) that encodes both encrypted premeasured characteristic responseand unique identifier information. In another variant of thisembodiment, visible indicia 308 are provided by a machine readable barcode (not shown) that encodes only unique identifier information.

FIG. 4 shows a security device 400. The security device 400 comprises aplurality of magnetic elements 402 formed upon a silicon substrate 404.The magnetic elements 402 are made of permalloy material. Each magneticelement 402 is backed by a reflective layer 410 made from gold,aluminium, chromium and/or tantalum, for example. The reflective layers410 provide enhanced reflectivity contrast between the magnetic elements402 and the substrate 404. This embodiment thus provides for an improvedsignal to noise ratio (SNR) when the security device 400 is beinginterrogated by a reading apparatus, such as, for example, a readingapparatus of the type described herein. An advantage of increased SNR isthat it enables such a security device 400 to be rapidly interrogated todetermine whether or not it is a forgery, and/or needs lower levels ofincident light (e.g. ultraviolet to infrared, such as, for example, from200 nm to 1500 nm) in order to be interrogated.

FIG. 5 shows a further embodiment of a security device 500 in plan view.The security device 500 comprises a plurality of magnetic elements 502a-502 e formed upon a silicon substrate 504. The magnetic elements 502a-502 e are made of permalloy material formed in the shape of wires, orflattened wires. The magnetic elements ends 505, 507 are formed asangled shapes.

In this embodiment, the width of the magnetic elements 502 a-502 e inthe direction A-A can be made of various widths. In this case, the widthof the magnetic elements 502 c and 502 e are approximately double thoseof magnetic elements 502 a, 502 b and 502 d. Since the magnitude of thecharacteristic response signal produced by any particular element isproportional to the volume of material that makes up that element,larger elements give rise to a larger signal that is accordingly moreeasily measured.

In addition, the magnetic elements 502 a-502 e can themselves be used toencode an identifier. In the illustrated embodiment, the five magneticelements 502 a-502 e occupy an area of approximately 1×1 mm with spaceenough for some seven to twelve magnetic elements of the 40 μm width and900 μm length of magnetic elements 502 a, 502 b and 502 d. The patternof the five magnetic elements 502 a-502 e is used to provide anidentifier for the security device 500. This pattern is analogous to abar code that identifies a particular security device 500, and may beunique to each individual security device 500 that is manufactured.

The number of unique identifiers that can be provided by variants ofthis embodiment depend upon the number and density of the magneticelements 502. For example, embodiments having a possible 32 magneticelements provide for a possible 2³² (i.e. 4,294,967,296) uniqueidentifiers. Moreover, where the magnetic elements are identifiableusing a two-dimensional scanning pattern, e.g. where magnetic elements502 are provided in an array of 32×32 dots, this figure can be squared.

FIG. 5 a illustrates another embodiment. Various magnetic elements 81,82 of different lengths are provided. In this embodiment acharacteristic response can still be measured even from what appear aspart of an identifier pattern as ‘spaces’, since the effective bits ofan identifier provided by the magnetic elements 81 each still provide aresponse. Reading is achieved using a laser beam that may only befocused in one dimension, e.g. to 1 mm long and 20 microns wide. Thereflected intensity, as measured e.g. using the magneto-optic Kerreffect as herein described, therefore changes according to the length ofthe bar. Typically 30 μM width bars with longer bars 82 about 700 μmlong and shorter bars 81, for example, some 300 mm long, may beprovided.

FIG. 6 shows an embodiment of a security device 600 in cross-sectionalview. Although this embodiment incorporates both reflectivity andcontrast enhancing materials, these can be provided separately invarious other embodiments.

The security device 600 is formed from a silicon substrate 604. Thesubstrate 604 incorporates reflective layers 603 formed beneath magneticelements 602 made from, for example, gold, aluminium, chromium and/ortantalum. The reflective layers 603 increase the optical signal(including the Kerr effect signal, as described below) reflected fromthe magnetic elements 602 as compared to magnetic elements formeddirectly onto a substrate material.

Adjacent to the magnetic elements 602 absorbing layers 605, made of, forexample, carbon, are formed. The absorbing layers 605 have a lowreflectivity, and thus enhance the contrast between light reflectedtherefrom and the adjacent magnetic elements 602.

Another variant of the embodiment shown in FIG. 6 uses, for example, aroughened surface formed by deposition or etching, as a scatteringmaterial in place of the absorbing layers 605. The effect of thescattering material is to attenuate any optical signal reflected fromthe areas adjacent the magnetic elements 602, with the additionaladvantage that the security device 600 need not absorb as much opticalenergy.

In order to characterise various materials that may have desirableresponses to an applied magnetic field, it is useful at this point todescribe some of the physics involved in the switching of themagnetisation direction of various types of ferromagnetic materials.Such ferromagnetic materials may be used in various embodiments.

Referring to FIG. 7 a, a magnetic element 102 is shown. In this example,the magnetic element 102 is formed of a ferromagnetic material shaped inthe form of a flattened wire. The magnetic element 102 has amagnetisation M having an initial magnitude and direction as indicatedby the arrow 150. An applied magnetic field H is shown being applied tothe magnetic element 102 in a direction substantially parallel to alongitudinal axis of the magnetic element 102, and with an oppositepolarity to the initial magnetisation.

The applied magnetic field H acts to reverse the polarity of themagnetisation of the magnetic element 102. There are various physicalmechanisms by which the magnetisation of the magnetic element 102 canreverse. Each of these leads to a different magnetic switchingcharacteristic of the magnetisation M.

In a first switching mode (sometimes referred to as a coherent rotationmode, shown schematically in FIG. 7 b) the individual magnetisations ofa plurality of magnetic domains 152 rotate coherently, as shownschematically by the broken arrows 154. Thus in this mode, the overallmagnetisation of the magnetic element 102 undergoes smooth directionalrotation and magnetisation magnitude changes to align with the appliedmagnetic field H.

In a second switching mode (sometimes referred to as a multiplenucleation mode, shown schematically in FIG. 7 c) many magnetic domains156 dominates the switching of the magnetisation of the magnetic element102 when an applied magnetic field H is present. The magnetisations ofthe individual domains 156 initially rotate into alignment with theapplied magnetic field H, as illustrated in FIG. 7 c. Subsequently thedomains grow in size. However, in this mode the temporal evolution ofthe magnetisation of the whole of the magnetic element 102 cannot bereadily discerned, and may change randomly in response to environmentalconditions, such as temperature.

Thus, although materials that operate according to the second switchingmode can be used for magnetic elements of various embodiments, they arenot optimal since, because there is less variation in the magneticswitching properties to provide a measured characteristic response, itis relatively easy to copy.

In a third switching mode (sometimes referred to as Brown's paradox, asharp switching or a brittle mode, shown schematically in FIG. 7 d) thegrowth of a single magnetic domain 158 dominates the change inmagnetisation of the magnetic element 102. Such a domain 158 may beassociated with a structural defect in the magnetic element 102 that israndomly introduced during a manufacturing process, e.g. byuncontrollable fabrication noise arising from random nano-scale materialdefects (e.g. defects that occur on a size scale from about 0.5 nm toabout 500 nm) that are virtually impossible to reproduce controllably orpredictably. In this mode, the growth of domain 158 dominates theswitching of the magnetisation of the magnetic element 102 over a widevariety of physical and environmental conditions. Accordingly, materialsthat operate according to the third mode are ideally suited to theprovision of stable, but non-predetermined, magnetic switchingproperties that provide a reproducibly measurable characteristicresponse.

Various possible defects can form a nucleation centre, these can, forexample, include one or more of the following: local failures inlithographic definition, e.g. small (micron or sub-micron) notches outof the edges of tips of elements; local crytallographic defects, such asdislocations, inclusions, nanometre-scale voids; local variations inchemical composition or stoichiometry, leading to a local change inmagnetic anisotropy; and local short-scale variations in thickness,leading to a surface indentation which can generate Orange Peel fields,as envisaged by Brown.

The reference ‘Introduction to the Theory of Ferromagnetism’ by AmikamAharoni (ISBN 0 19 851791 2), pp. 204-214, gives a useful overview ofmany of the aforementioned concepts.

FIG. 8 a shows an idealised single hysteresis loop 160 indicating howthe magnetisation M of a magnetic element 102 made from the permalloymaterial varies as a function of an applied magnetic field H. Dottedlines 169 indicate how the idealised single hysteresis loop 160 may varyfrom the ideal for a real magnetic element 102. The magnetic element 102starts with an initial magnetisation 172. The applied filed H isincreased until it reaches a value 170. Thereafter, the applied field His increased to a switching value 168 where, due to hysteresis, themagnetic element 102 rapidly switches its magnetisation M from theinitial magnetisation 172 to a magnetisation 164. Thereafter, theapplied field H is decreased to a switching value 174 where, due tohysteresis, the magnetic element 102 rapidly switches its magnetisationM from the magnetisation 164 back to the initial magnetisation 162.

As is observed from FIG. 8 a, the magnetic switching characteristics ofthe magnetic element 102 made from permalloy material is seen to operatein the sharp switching mode, even when the real hysteresis loops deviatefrom the ideal, as the transitions of the magnetisation from onepolarity to the other are still sharply defined.

FIG. 8 b illustrates an averaged hysteresis loop 180 for many (e.g.˜100) cycles of the magnetic element 102 made from the permalloymaterial around hysteresis loops of FIG. 8 a. It is observed that theaveraged hysteresis loop 180 does not show sharp transitions in thestate of magnetisation of the magnetic element 102, even though sharptransitions do occur for each individual magnetic cycle 160. The reasonfor this is because the switching values 168 and 174 of each individualmagnetic cycle 160 vary between cycles which gives rise to jitter.

The magnitude Δ of the jitter 196, determined as the standard deviationof the differences in switching values 168 for the various magneticcycles 160, is shown in relation to the averaged hysteresis loop 180. Inturn, the jitter magnitude Δ provides a characteristic response for themagnetic element 102 that generates it. The magnitude of the jitter isdependent on the precise volume and energy of the nucleation centre thatis responsible for magnetisation reversal. It therefore varies from onemagnetic element to another, since no two nucleating defects are likelyto be the same.

Coercivity is also a characteristic measurement that indicatesuniquenss. In various embodiments coercivity provides for a bettercharacteristic response than jitter. In such embodiments jitter can bemeasured as an additional characteristic response parameter. Viewed fromone perspective, a distribution function representing thereversal/switching field (of a single magnetic element) as observedacross many reversals/switchings has a central value of the distributioncorresponding to the coercivity and a width distribution representativeof the jitter.

Various embodiments of a security device incorporating magnetic elementscan be provided. One process of manufacturing various of such securitydevices on a silicon substrate using optical lithography will now bedescribed, by way of example.

The manufacturing process is illustrated in FIGS. 9 a to 9 h. Theprocess starts in FIG. 9 a with a cleaned and polished silicon wafer704. In various embodiments, the silicon substrate is approximately 0.5mm thick in order to facilitate handling and provide a rugged securitydevice. A photoresist layer 714 is spun onto the wafer to provide asmooth coating as shown in FIG. 9 b. The wafer and photoresist layer 714are then baked to set the photoresist layer 714.

FIG. 9 c illustrates the device of FIG. 9 b post-exposure to UVradiation or near-UV radiation (e.g. at 405 nm). The regions 708represent exposed regions. The exposed regions 708 are directly writtenonto the upper surface 701 of the photoresist layer 714 using acommercially available direct write scanning optical lithography systemsuch as, for example, a NanoMOKE2 system with a LaserWriter add-onsupplied by Durham Magneto Optics Ltd. In this way, an individualone-dimensional or two-dimensional pattern can be written into thephotoresist layer 714 for each security device that is manufactured.This pattern may define a plurality of wire shapes, such as, forexample, those illustrated in FIG. 1.

FIG. 9 d shows the device of FIG. 9 c after is has been developed toremove exposed photoresist 708. Removal of the exposed photoresist 708exposes portions 710 of the underlying silicon substrate 704.

Subsequently, as shown in FIG. 9 e, magnetic elements 702 formed of apermalloy material such as, for example, Ni₈₀Fe₂₀ (see, for example,Bozorth, Ferromagnetism, ISBN 0-7803-1032-2, for further information)are deposited in exposed portions 710 by a sputter deposition orevaporation process, typically to a thickness in the range from about 10to about 100 nm, e.g. to about 40 nm. Further layers 712 of permalloymaterial also form on the remaining unexposed photoresist 706 during thesputter deposition process.

Next, metal capping layers 716, 718 of gold or aluminium are formed overthe permalloy layers 712 and magnetic elements 702, as illustrated inFIG. 9 f. The capping layer 718 is designed to protect the permalloylayer from oxidation and also provides an enhanced optical reflectivity.

The unexposed photoresist 706 along with overlying permalloy layers 712and capping layers 716 are removed using a suitable solvent, e.g.acetone, to leave the structure illustrated in FIG. 9 g. The resultingstructure comprises the magnetic elements 702 formed on the siliconsubstrate 704 separated by exposed silicon substrate regions 720. Theupper surfaces of the magnetic elements 702 are capped by capping layers718.

The aforementioned resulting structure is placed into a plasma enhancedchemical vapour deposition (PECVD) chamber where a silicon dioxide(SiO₂) layer 722 is deposited upon the upper exposed silicon substrateregions 720 and capping layers 718. The silicon dioxide layer 722 formsan optically transparent layer (including, inter-alia, a layer that issubstantially transparent to infra-red electromagnetic radiation). Theresulting security device 700 is shown in FIG. 9 h.

Where several security devices 700 are manufactured upon a singlesilicon substrate 704, the silicon substrate 704 can subsequently bediced into a plurality of individual security devices 700.

The applicants have produced several prototype security devices usingthe process hereinbefore described. During production of these prototypesecurity devices the sputter deposition process parameters used were asfollows: 250W power setting; base pressure 5×10⁷ mbar; Argon gas; gaspressure 1 to 2 mTorr; flow of 5 cc/minute; substrate rotation rate 10rpm; deposition rate 1 to 1.5 Angstroms per second; and a substratetemperate of 22 to 27° C. It is also possible to apply a magnetic fieldalong the plane of the device during the manufacturing process.

The applicants note from an analysis of their prototype securitydevices, that fine tuning of the growth rate and/or sputter pressure forthe magnetic elements can provide improvements to sharp switching modemagnetic switching characteristics. The applicants have also noted froman analysis of their prototype security devices, that magnetically softmaterials tend to give rise to desirable magnetic switching properties.

Once a security device had been manufactured it is tested, either aloneor as part of a batch of such security devices, to determine itscharacteristic response. The characteristic response is measured toensure it provides for adequate identification of the particularsecurity device.

Magnetic elements are first tested to determine whether or not theyoperate in the sharp switching mode. A Kerr magnetometer, as describedin Applied Physics Letters, Vol. 73, p. 3947, 1998, is used to measurethe coercivity at a number of points on each individual magneticelement. For example, five points on each element may be used and thecoercivity measured at each point. Magnetically sharp switching isdeemed to exist if the variation between measured coercivity values fromone magnetic element is small compared with the variation betweencoercivities measured across a number of elements. In practice,magnetically sharp structures switch with less than 0.2 Oe variationacross the element, while one element may differ in coercivity fromanother by approximately 1-2 Oe.

A jitter measurement may also be made for each magnetic element, or fora group of such elements, by repeating measurements on thatelement/group and determining how much the coercivity varies betweensets of measurements. These sets of measurements are repeated many timesfor each magnetic element/group of the security device. In one example,coercivity may be measured at one point on a security device, onehundred times per each magnetic element/group of magnetic elements atroom temperature. The measured coercivity values are then fitted to aGaussian bell-curve, and the mean coercivity and jitter (as indicated bythe mean and standard deviation Δ of the fitted Gaussian curve,respectively) calculated.

The applicants have found that for various embodiments, over a typicallikely operating temperature (for example, from −20° C. to 50° C. whereanti-misting measures are provided in a reader), jitter exhibited only aweak temperature dependency.

In various embodiments, there is a measurable dependence of meancoercivity on temperature. However, provided that the mean coercivity ofa plurality of magnetic elements varies in the same way withtemperature, the coercivity differences between magnetic elementsremains almost constant. Thus, when comparing the measured meancoercivity against the premeasured characteristic response, an allowancemay be made for a constant offset between the two sets to compensate fordifferent temperatures.

However, if desired or required for various other embodiments,coercivity and jitter measurements may be made at several temperatures,including temperatures outside a normal operating temperature range. Forexample, sets of measurements could be made on each magnetic element at−50° C., 0° C. and 65° C. for a security device rated for operation fromabout −20° C. to about 50° C.

In practice, an upper limit on the permitted variation allowed betweenthe measured coercivity values measured for a single magnetic elementshould be set. This can be an absolute value (e.g. 0.2 Oe) or bedetermined relative to the jitter magnitude (e.g. 10% of the measuredjitter value). Security devices having one or more magnetic elementsthat gave rise to coercivity variation values greater than the permittedvariation should be rejected.

A desirable characteristic is that any variation due to jitter be smallin order that the mean coercivity be easier to measure. Mean coercivitycan then be used as a parameter for a premeasured characteristicresponse. Jitter may also be used as parameter for the premeasuredcharacteristic response, e.g. in addition to mean coercivity forrespective magnetic elements or groups of such elements.

In various embodiments, security devices may have their premeasuredcharacteristic response defined by a mean coercivity value and/or ajitter value Δ, for various magnetic elements or groups of magneticelements. Various other embodiments use, for example, either a meancoercivity value or a jitter value to represent a premeasuredcharacteristic response. In use, the premeasured characteristic responseof a security device is compared to its measured characteristic responseto determine if that security device is a forgery.

The premeasured characteristic response can be encoded, for example, bydigitising the values of the mean coercivity and/or the jitter value Δ.In various embodiments, these values are stored in encrypted form uponthe corresponding security device, either with or without an identifierthat may be unique. In various other embodiments, these values arestored separately from the corresponding security device. In variousembodiments, during a reading operation (as described below) thedigitised values of mean coercivity and/or jitter value A representing apremeasured characteristic response can be retrieved/recovered for aparticular security device and compared to measured values of meancoercivity and/or jitter value A for a security device purporting to bethe same device, so as to determine whether or not the security devicewhose characteristic response has been measured is a forgery.

Security devices may be attached to articles in order to aid inidentifying such articles as genuine or non-counterfeit. In use it isnecessary to read the characteristic response of a particular securitydevice in order that it may be compared to a premeasured characteristicresponse, such as for example, a baseline response. Any differencesbetween the measured and premeasured response, outside of any allowablelimits, indicate that the security device that has been read is aforgery. Since the production of magnetic nucleation centres is beyondthe control of the manufacturer, any copying of the device will almostinvariably result in a different characteristic response, such as, forexample, mean coercivity and jitter values.

Various embodiments of systems, both hand-held or otherwise areenvisaged. Various such embodiments are described below in connectionwith FIGS. 10 to 17 of the drawings.

FIG. 10 shows a reading arrangement 930 forming a component of asecurity device reading system for obtaining a measured characteristicresponse of a security device 900 while the security device 900 issubject to an applied magnetic field 932. The reading arrangement 930can detect changes in the polarisation of light reflected from themagnetic elements using the magneto-optic Kerr effect (MOKE).

The reading arrangement 930 comprises an aluminium block 934 whoseinternal and external surfaces are blackened using a black mattanti-reflection paint. The size of the an aluminium block 934 istypically 2 cm×2 cm×1 cm. The aluminium block 934 comprises beam pathchannels 938, 940, 942. A near infra-red or visible laser diode 936,which is provided with collimating optics (not shown), is operable toproduce a collimated laser beam 944 at a wavelength of, for example, 600to 1550 nm. One embodiment uses a laser diode operating at 670 nm. Thelaser beam 944 passes though a first beam path channel 938, before itleaves the aluminium block 934 and is incident upon a mirror 950.

The laser beam 944 is reflected from the mirror 950 into a second beampath channel 940 formed in the aluminium block 934. A polariser 952placed into the second beam path channel 940 converts the laser beam 944into a plane polarised laser beam 947. The plane polarised laser beam947 then leaves the second beam path channel 940.

The aluminium block 934 also comprises a third beam path channel 942.The third beam path channel 942 is oriented so as to collect reflectedlight 949 that is reflected from a security device 900 when being read.Typically, if a security device 900 has wire-shaped or flattenedwire-shaped magnetic elements 902, the applied field 932 is applied in adirection substantially parallel to the axis of the magnetic elements902.

An analyser 954, used in various embodiments, incorporating an optionalquarter wave plate and polariser is placed into the third beam pathchannel 942. The analyser 954 passes light of a first polarity andblocks light of a second an orthogonal polarity. Light of the firstpolarity is reflected from a magnetic element 902 when it is in a firstsaturated magnetisation state, and light of the second polarity isreflected from the magnetic element 902 when it is in a second saturatedmagnetisation state having a largely reversed polarity or modifiedintensity with respect to the first magnetisation state.

The polariser 952 and the analyser 954 are arranged to measure thelongitudinal magneto-optic Kerr effect signal produced when the planepolarised laser beam 947 is incident upon the magnetic elements 902.Other magneto-optic Kerr effect arrangements, for example, includingarrangements without a polariser and/or analyser and/or using atransverse or polar arrangement may also be used. However, a benefit ofusing a longitudinal magneto-optic Kerr arrangement is that it generallyprovides an improved signal as compared to transverse or polararrangements.

Aligned with the third beam path channel 942 is a detector unit 956,which in this embodiment incorporates a focussing lens and a photodiodecircuit or phototransistor circuit sensitive to illuminating radiation.The photodiode circuit is responsive to light transmitted through theanalyser 954 to provide a signal proportional to the magnetisation ofany magnetic elements 902 illuminated by the plane polarised laser beam947.

FIG. 11 shows a mirror actuator 969 for moving a mirror 950. Such amirror actuator 969 may be used in conjunction with the readingarrangement 930 described herein. The mirror actuator 969 comprises anelectromagnet 971 operable to deflect a mild steel deflecting element982 attached thereto. The electromagnet 971 comprises a first actuatorcoil 986 wound onto a first region of a magnetic core 980, and a secondactuator coil 988 wound onto a second region of a magnetic core 980. Themagnetic core 980 includes a gap 992 at which, when the electromagnet isenergised, a magnetic deflecting field is produced.

The deflecting element 982 is connected to the magnetic core 980 by wayof a threaded bolt 984. Tightening of the threaded bolt 984 secures thedeflecting element 982 to the magnetic core 980 proximal one end of thedeflecting element 982. An unsecured end of the deflecting element 982distal the threaded bolt 984 is thereby able to move with respect to themagnetic core 980 under the influence of the magnetic deflecting fielddue to the attractive force generated between the magnetic deflectingfield and the mild steel material of the deflecting element 982. Themirror 950 is mounted upon one part of the deflecting element 982 andmoves in response to movement of the deflecting element 982.

In operation, an energising current is passed through the first andsecond actuator coils 986, 988. The first and second actuator coils 986,988 can be connected in series such that the same energising currentpasses through both coils. Passing an initial energising current throughthe first and second actuator coils 986, 988, causes the deflectingelement 982 to deflect in the direction shown by arrow 990, thereby alsodeflecting the mirror 950.

FIG. 12 shows a field generation system 935, a detection system 937, acontrol and processing system 939 and a beam scanning system 941forming, in conjunction with the reading arrangement 930 describedabove, a further part of one embodiment of a security device readingsystem.

The field generation system 935 comprises components for producing atime varying applied magnetic field 932 for applying to a securitydevice 900. The field generation system 935 comprises a driver circuit966 operable to drive field generation coils 933 a, 933 b in response toa coil driving signal 970. The coil driving signal 970 is a periodicsinusoidal signal composed of a plurality of individual sinusoidalwaveforms 972 oscillating at a frequency of 100 Hz (see FIGS. 13 and15), that drives the drive field generation coils 933 a, 933 b toproduce a sinusoidinally oscillating magnetic field oscillating at 100Hz. In this embodiment, the 100 Hz sinusoidal waveform is produced by aconventional electronic oscillator circuit (not shown).

The field generation system 935 additionally comprises a cross-overdetector 968 for detecting polarity changes in the coil driving signal970. The cross-over detector 968 produces a synchronisation signal 981in response to being driven by the driver circuit 966, as shown in FIG.17. The synchronisation signal 981 is composed of a sequence of spikes983 each produced at a time when the polarity of the coil driving signal970 changes. In various other embodiments, the same microcontroller thatlogs the Kerr signal is used to generate the applied field sequence (viaa Digital to Analogue Converter), so the microcontroller can controlsynchronisation therebetween.

The detection system 937 comprises detector unit 956 for producing asignal in response to incident light 948. The detector unit 956 iscoupled to an amplifier 958. Signals produced by the detector unit 956are amplified by the amplifier 958 to provide a unipolar detector signal973 (see FIG. 16). The unipolar detector signal 973 is then fed into ananalogue to digital converter (ADC) 960 for digitisation. The ADC 960 isa 10 bit device operating at a 10 kHz sampling frequency; thereby giving1024 possible discrete data levels for each of the 100 samples takenover the time taken for one cycle of a 100 Hz cycle to complete.

In one embodiment, the ADC 960 operates at 10 kHz and acquires around100 data points per applied magnetic field cycle. The applied field isapplied at a frequency of around 10 kHz/100=100 Hz. Data is averaged foraround 0.5 sec, i.e. there are 50 data sets averaged for a singlemagnetic element. From this mean coercivity and jitter are measured. Theprocess is then repeated for another magnetic element. In total around 8magnetic elements are analysed in this way.

The control and processing system 939 is used to acquire measured datarepresentative of the characteristic response of the security device 900from the detection system 937, analyse that measured data and compare itwith a premeasured characteristic response to determine if the securitydevice 900 is genuine. In various embodiments, the control andprocessing system 939 also controls a beam scanning system 941 to causethe plane polarised laser beam 947 to move across the surface of thesecurity device 900.

The control and processing system 939 comprises a processing unit 962having an associated data store 974. In various embodiments, theprocessing unit 962 comprises a microprocessor or microcontroller andassociated memory (not shown), including a ring buffer to which datasamples from the ADC 960 are constantly fed when the ring buffer isenabled by the microprocessor.

When the security device reading system is started, the ring buffer isdisabled by the microprocessor. In order to begin accumulating data intothe ring buffer, a first spike 983 is received by the microprocessor.This triggers the microprocessor to begin a count of the number ofsynchronisation spikes 983 that are received and simultaneously toenable the ring buffer. Thus, data begins accumulating into the ringbuffer in synchronisation with a polarity transition occurring in theapplied magnetic field 932. When the microprocessor detects the Nthspike 983 (e.g. the 100th), a signal is sent to inhibit furtheraccumulation of data into the ring buffer. The ring buffer at this timewill contain N sets of data each accumulated during one half cycle ofthe applied magnetic field 972, with each set of data representing adigitised respective portion 975, 977 of the unipolar detector signal973 at a respective time during the time duration t (t=N×appliedmagnetic field frequency/2) of the data accumulation. (e.g. t=0.5 secondduration for 100 cycles at 100 Hz with N=100, and 5,000 individualmeasurements are made with an ADC rate set to 10 kHz).

For an embodiment that includes a beam scanning system 941 coupled to amirror actuator 969, a processing unit 962 can also be used to providecontrol signals for moving the position of a mirror 950. The beamscanning system comprises a driver circuit 964 which includes a digitalto analogue converter which sets the current provided through the firstactuator coil 986 and the second actuator coil 988. The switchingcircuitry is configured to connect the first and second actuator coils986, 988 in series, and to apply a driving current in proportion to acontrol voltage 994 (see FIG. 14) provided by the processing unit 962.

In one embodiment, the ring buffer accumulates several sets comprising Nsets of data. Once a set of N sets of data has been accumulated, thering buffer is disabled by the microprocessor until the N sets of datahave been stored in the store 974. The processing unit 962 thenincreases the control voltage 994 to cause the mirror 950 to deflect aplane polarised beam 947 onto a further area of the security device 900.After a short delay period to allow the mirror actuator 969 to settle,the microprocessor awaits a first spike 983 and subsequently begins toacquire the next N sets of data. This process continues until N sets ofdata have been accumulated and stored for each position of the mirror950.

As indicated above, data sets can be accumulated in a variety ofmanners. Once acquired, the data can be processed to extract a varietyof information regarding the measured characteristic signal response.Standard algorithms can be applied to the data sets to calculate themean measured coercivity and/or jitter as given by a measure of thestandard deviation of coercivity measurements. Examples of suchalgorithms may be found, for example, in “Numerical Recipes in C: TheArt of Scientific Computing,” W. H. Press, S. A. Teukolsky, W. T.Vetterling and B. P. Flannery, (Cambridge University Press, Cambridge,1993).

Data fitting can either be done by the samemicroprocessor/microcontroller that determines the measuredcharacteristic signal response, or by a connected computer system. Forexample, where a remote data base stores the premeasured characteristicresponse, raw measured characteristic signal response data can betransmitted to a remote processor to perform a Gaussian fitting.Similarly, where used as part of a fraud detection system, a reader maybe connected to a Palm-top computer which stores premeasuredcharacteristic response data by downloading it from the internet, andcompares it to the measured characteristic signal response. In variousembodiments, Palm-top computers can be used as the interactive displayof the reader and also as a means of accessing remote data bases, e.g.by using GSM telephones.

Various ways exist for determining the premeasured characteristicresponse of a security device. These ways vary according to the type ofsecurity device and depend, for example, on whether or not thepremeasured characteristic response is stored/encoded on the securitydevice; whether or not the premeasured characteristic response isencrypted; and whether or not a unique identifier is provided inassociation with the security device. All these possibilities providefeasible embodiments.

In various embodiments, a unique identifier and an encrypted premeasuredcharacteristic response, comprising encoded data representing a meancoercivity and a standard deviation in measured jitter, are encoded ontoa security device as a sequence of pits. The pits are formed in adirection co-linear with a beam scanning direction, as provided by abeam actuator 969. Prior to determining the measured characteristicresponse, the beam actuator 969 is driven to provide a beam at points onthe security device where the pits are anticipated to be. At each suchpoint, a signal from detector unit 956 is measured. High reflectivityindicates a logical zero for the data bit corresponding to therespective point, and low reflectivity indicates a logical zero.

Of course, the plane polarised laser beam 947 of various embodiments maybe focussed using a lens system to provide a small focal spot size at asecurity device 900. Similarly, collecting optics may be provided in thebeam path channel 942 to aid in collecting light reflected from thesecurity device 900.

In various other embodiments, a smart card carries a security device andunique identifier and an encrypted premeasured characteristic responseinformation are stored in the smart card. The smart card is read in aconventional manner and a measured characteristic response is measuredas herein described.

In certain embodiments the magnetic elements of a security devicethemselves may be used to encode further information. They can, forexample, encode a unique identifier by forming a pattern of shapes. Suchsecurity devices may be scanned to see firstly if any magnetic elementsare present at various possible locations. A linear scan pattern ofreflected signal can then be used to obtain a binary value identifierfor the security device. A way of visualising this is to consider thepattern of the magnetic elements to represent a form of bar code.

For embodiments of a security device comprising magnetic elements thatencode a unique identifier, a characteristic response may be measured,as hereinbefore described, for each individual element. Various readersmay however only measure the characteristic response for a subset of themagnetic elements in order to speed up the reading process.

In an embodiment of a security device reading system, premeasuredcharacteristic response information is stored in a database to which oneor more processing units have access. The premeasured characteristicresponse information is preferably encrypted. Such a system may bedistributed and comprise a remote server coupled through a network toone or more security device readers. A system according to thisembodiment is operable to determine a unique identifier for eachsecurity device from the pattern of the magnetic elements, or by othermeans, and to retrieve premeasured characteristic response informationcorresponding to the unique identifier determined by the security devicereading system. The premeasured characteristic response information canthen be decrypted as necessary by a respective security device reader.

In embodiments of the security device reading system, once theinformation regarding the measured characteristic signal response hasbeen extracted it is compared by the microprocessor to the premeasuredcharacteristic response, possibly decrypted using a private asymmetricdata key, to determine whether or not the security device can be classedas non-counterfeit. Such a comparison is made within a margin of errorallowed for variations that are introduced, for example, by temperaturefluctuations. For example, for mean coercivity/jitter this may be whenthe measured coercivity/jitter does not differ from the premeasuredcoercivity/jitter by more than one standard deviation of thedistribution of mean coercivity/jitter values.

Referring to FIGS. 18 to 20, illustrations of three example structuresof magnetic elements are provided in plan view.

In the first, a collection of regular rectangular magnetic elements (1)is shown schematically and not to scale. The material of the elements isNi₈₀Fe₂₀. The material is laid down to a thickness of 40 nm. The overallarea of the signature portion is 1 mm by 1 mm. The illustration isschematic only and not to scale. In particular it should be appreciatedthat each 1 mm by 1 mm area will comprise a very large plurality ofelements of micron-scale width.

Moreover, any representation that the elements are of equal widths isschematic only. An array of 1 μm wide wires might be suitable for someapplications. However, as has been noted above, any array of discretegroups of different wire width giving several discrete switching fields(for example as above described), or a continuously varying array withwidth varying in linear or other functional manner (for example as abovedescribed), will often be preferred.

FIG. 19 shows a generally similar structure having generally similardimensions. The caveats above about the schematic nature of theillustrated widths again applies. However, in this instance, therectangular portions (2) do not have square ends, but are provided withpointed ends. Differently shaped ends can affect the switching field andthus be preferred for certain applications. Any suitable end shape canbe made use of without departing from the principles of the invention.

On FIG. 20 a yet further alternative is shown, the signature portioncomprising a generally square 1 mm by 1 mm array of circular magneticmicrodots (3). In this instance material thickness is around 100 nm.Each microdot is 100 μM in diameter. Again this is illustrative only.Alternative shapes can be considered, and again elements of discretelyor continuously varying size and/or shape, provided the basicrequirement for a device in accordance with the invention that areproducibly measurable baseline signature response is obtainable ismet.

The film is laid down by any suitable method, in particular by opticallithography such as using the method herein described.

FIG. 21 illustrates a mechanical drawing of an example of a small devicesuitable for measuring the magnetic response of a small area of thinmagnetic film, such as a magnetic film comprising a magnetic signaturein accordance with the invention, for example the signatures illustratedin FIGS. 18 to 20.

The device to measure the magnetic response comprises a high intensitylight source, in this instance an infra-red light emitting diode withinthe housing (11). The light is collimated by a single pin-hole (12), ofdiameter in the size range 0.2 mm-5 mm. The light is then reflected offthe surface of the magnetic thin film placed in position (15) against itand passes through a second pin-hole (13), with diameter in the sizerange 0.2 mm-5 mm, and preferably of the same diameter as the firstpin-hole.

The reflected light then passes into a light sensitive device within thehousing (14), which is by preference a phototransistor or photodiodesensitive to infra-red radiation. In this illustrated embodiment thelight sensitive device is selected to have low sensitivity to visiblelight, allowing the device to be used without optical screening. Thedevice may also be painted black to reduce stray light reflections.

Magnetic field coils (not shown) are attached to the device to applymagnetic fields in the range 0-500 Oe to the magnetic material undertest. In the case of the magnetic material under test comprising anarray of elongated elements, such as rectangles, by preference themagnetic field coils are oriented so as to apply a field in the plane ofthe film and either along the long-axis of the elongated structures orat an angle to the long-axis in the range 0°-60°. Additional magneticfield coils can be present to apply an additional field transversely tothe long-axis of the wire.

The phototransistor or other light receiving device is connected tosuitable electronics (not shown) which record the reflected intensityfrom the magnetic material while an alternating current is passedthrough the coils generating the applied magnetic field. Signalprocessing electronics using a Digital Signal Processor chip or aMicrocontroller chip record measured responses over a number of cyclesof the applied magnetic field and add them together coherently to reducenoise. The number of cycles recorded will be such that the totalacquisition time does not exceed 10 seconds, and for convenience willnot exceed 5 seconds. The signal processing electronics then identifiesthe mean switching field for each of the major switching transitions inthe recorded signal. These are then passed to other electronics (notshown) which acquire and if necessary deciphers the prerecorded baselineresponse from a magnetic strip, smart card, optical bar code, or from aremote textual source or electronic data store or other means, oralternatively transmits the measured response to a remote datacomparator having access to the prerecorded baseline response, and acomparison is made.

FIG. 22 illustrates the application of the present invention to a smartchipped card of otherwise generally conventional design. The card (21),typically sized and shaped as a credit card or the like, and which mayindeed be used as a credit card or the like, is illustrated in plan viewboth from above (A) and from below (B). The card carries somealphanumeric information, but its main information storage system is thesmart chip (22). This is backed up by optional bar code (23), andmagnetic stripe (24) which is typically provided for backwardcompatibility with magnetic stripe only systems.

A magnetic signature device (26) comprising a 1 mm by 1 mm array ofmagnetic elements of appropriate design in accordance with the inventionis applied on the rear of the smart card. For convenience, in theexample shown, it sits within the foot print of the smart chip itself asillustrated by the broken line (28). For many applications it might beconvenient to sit the magnetic element (26) within this footprint. Analternative approach to achieve the same effect might be to incorporatethe relatively small 1 mm wide magnetic signature device into aspecially enlarged space between contacts on the smart chip. However,such placement is purely for convenience, and the magnetic elements (26)could be placed elsewhere on the card.

At the time of manufacture of the card an initial baseline signaturereading is taken. One way of doing this is to use a scanningmagnetometer. In the illustrated embodiment of a smart card, thebaseline response is stored on the card, having first been digitallysigned using an asymmetric encryption algorithm such as RSA. The publickey can then be made available to a user and/or stored on a readerterminal or even on the card itself without compromising security. Thesignature can then be used to verify that the card is a genuine productof the manufacturer, and to eliminate the threat of fraudulent misuse ofcloned copies of the card, which constitutes an increasing source ofboth financial transaction fraud and identity fraud.

In use, the card is read by a suitable card reader, in particular by acard reader incorporating a signature device reader such as thatillustrated in FIG. 21. The device reader may be incorporated into anexisting smart card reader. For example, with the embodiment shown, thereading device for the magnetic element needs to read opposite side ofthe card from that read by the smart card reader, and so can beincorporated into a conventional smart card reader with relativelylittle engineering difficulty. In this way, cards and readers remainbackwards compatible to conventional card/reader technology not havingthe identification and authentication system herein described.

The reader measures an actual response from the card. An expectedbaseline response is also stored upon the card. This can be stored inany readable form, but is conveniently incorporated into the card in oneof the existing data storage devices. For example, the baselinesignature may be recorded in its encrypted form on the smart chip (22),the bar code (23) or the magnetic strip (24). The reader is thus able toread both the actual magnetic signature and the predetermined andprerecorded expected magnetic signature. The reader is adapted tocompare these, within certain tolerance limits, and to indicate whetherthe card is authenticated or not as a result of that comparison.

The smart card in accordance with various embodiments of the inventionwill be applicable to all circumstances where conventional smart cardtechnology is being used, including without limitation bank and creditcards, secure information storage cards, identification andauthentication cards and the like. It provides a means of authenticatingthe card as genuine, and thus provides a significant obstacle tofraudulent misuse of counterfeit copies of original cards.

The system represented by the embodiment in FIG. 22 is a simple system,in which a device in accordance with various embodiments of theinvention serves merely to authenticate the card as a genuinemanufactured product and thus to detect counterfeit copies, and inconsequence the predetermined baseline response is conveniently storedupon the card. It will be readily understood that such a system is onlyan example mode of operation. In one alternative, the original“expected” signature could be stored elsewhere. For example, in relationto the use of a card as illustrated in FIG. 22 as part of a financialservices system, for example as a credit card, a system can be envisagedwhere a plurality of cards are in issuance, where a plurality of readersare in use, and where the readers comprise a distributed network with acentral data store such as will already hold customer details beingfurther adapted to process signature information for verificationpurposes in accordance with the principles herein described. Other modesof operation will also readily suggest themselves.

In FIG. 23 an illustration is provided of the use of an embodiments ofthe present invention in a lock and key arrangement. A key card (31) ofsuitable robust material, for example of a suitable plastic material, isprovided with a device (36) comprising a 1 mm by 1 mm array of magneticelements as previously described.

The key card is provided in association with a card reader/lockarrangement illustrated schematically by the remainder of FIG. 23.

The lock (32) incorporates a slot (33) into which the end of the keycard (31) can be received. When appropriately positioned therein, thedevice (36) sits adjacent a reader (34) of the general designillustrated in FIG. 21.

The reader (34) obtains a reading of the magnetic response from thedevice (36) in the predescribed manner, and passes this response to acontrol unit (35). The control unit (35) stores or otherwise has accessto the predetermined expected response, for example storing this withinthe lock, optionally in encrypted form. It effects the comparison, andin the event that a match is found within predetermined tolerances,passes an instruction to the control means (38) to actuate the locklevers (39) and open the lock.

Although the example illustrated in FIG. 23 is an electromechanicallock, it will of course be understood that the principles of the presentinvention are equally applicable to all circumstances where a physicalor a virtual locking means or other means of access control might beconsidered. For example, without limitation, a device along the lines ofthe embodiment illustrated in FIG. 23 could be used in conjunction withan electronic lock for a door or other closure, in conjunction with anelectronic ignition for a vehicle, in conjunction with an electronicimmobiliser for a vehicle, as a means of controlling access to a pieceof electronic equipment, for example by requiring insertion before theequipment operates, as a means of restricting access to a particularservice etc.

In the illustrated embodiment, a single card is illustrated inassociation with the lock. In practice, even for simple single-userlocks it is likely to be necessary to provide several keys. It is in thenature of the present invention that these will inherently havedifferent signature devices. Accordingly, the lock would need to storeand respond to baseline signatures for each of these devices. Morecomplex modes of operation can also be envisaged where a lock providesfor access for a plurality of users, or indeed where a plurality oflocks are provided in association with a plurality of users.

In a first example of such operation, a plurality of locks and aplurality of keys are provided in association with a multiple use entrysystem into a secure area. In a second example of such a mode ofoperation, a plurality of operator cards are provided to controloperation of multiple user office equipment. In these examples, allauthorised base line signatures may be stored on each lock, oralternatively the locks may be linked together on a distributed networkto a central database storing details of the cards of all authorisedusers. Such a system allows not only good security because of thedifficult of producing counterfeit cards, but also allows control andmonitoring of access in an active way.

A further embodiment of the invention is illustrated in FIG. 24. In FIG.24, a signature device in accordance with the invention (46) isincorporated on a label attachable to an item to beidentified/protected. The label comprises a plastic tab (41) whichoptionally incorporates alphanumeric information; a bar code (44) etc.to store, for example identification information, information of origin,pricing information or the like about item to be labelled. The tab (41)is attached to an item to be labelled by the attachment strap (42). Inthe embodiment illustrated, the attachment strap (42) is intended as asimple loop attachment. Attachment may be releasable or permanent. Wheresecurity and permanence of attachment of the label are of particularimportance a more complex attachment would be readily envisaged whichmight for example include locking mechanisms, tamper preventionmechanisms, tamper indication mechanisms and the like.

The embodiment of FIG. 24 allows labelling of items in either atemporary or permanent manner where it is not practical or desirable toincorporate a device in accordance with the invention directly onto theitem itself Example modes of use include without limitation improvedsecurity airline luggage labels, authenticity labels for high valuebranded items, in particular clothing and the like; origin and identitylabels for the same, for stock control purposes, and for example foridentifying original and hence controlling unauthorised importation ofgenuine branded articles intended for another market; marking of itemsfor stock control purposes; price marking of items, labels being used insuch a way as to make it difficult for a purchaser to transfer a (lower)price label from another item to obtain goods at a fraudulently lowprice.

The normal mode of operation of a label of the type illustrated in FIG.24 will be authentication. Accordingly, the prerecorded signatureinformation will usually be stored on the tab (41). The prerecordedinformation will be stored in any suitable machine readable form. In theexample given it could be incorporated in the bar code. A reader will beprovided adapted to read both the magnetic signature of the device (40)and the encrypted expected signature, and to effect a comparison toauthenticate the label. The security effectiveness of the label lies inthat it is very difficult to copy, since the random nature of thesignature means that a copied label will be immediately identifiable assuch.

FIG. 25 illustrates a data storage disk such as a CD, DVD or the like towhich a device in accordance with the invention has been applied. Thedisc (51) incorporates a magnetic signature tab (56) comprising magneticelements as above described preferably within the dead area (53) nototherwise carrying data. An encrypted predetermined reading of thesignature (56) is provided elsewhere on the disc.

At its simplest, in a first mode of operation, the system allows themanufacturer to authenticate original CDs/DVDs, to identify counterfeitcopies, and in association with a suitable stock control system to trackorigin and destination of genuine originals, and to identifyunauthorised importation and the like.

In a more advanced mode of operation, disc readers can be manufacturedwhich incorporate device readers to read the device (56) and toauthenticate the disc, and which will be disabled from playingunauthorised copies. It is also possible to envisage a system wherebysuch modified players can be used in conjunction with theidentification/authentication system of the invention as part of an enduser licence arrangement.

FIG. 26 is an example of the use of the invention on a formalidentification document. Such a document might be an identification orauthorisation document, such as a passport, driver's licence,authorisation or qualification certificate or the like, an identity orauthorisation certification intended to accompany, verify or otherwiseidentify an article, or any other document where counterfeit copiesmight be a problem.

The document (61) in the example includes visual information (62), forexample a photograph, written information (63), and a bar code (64). Itmight include other data storage or security devices.

A device comprising magnetic elements as above (66) is incorporated intothe document. This device is readable in the manner above described. Inone mode of operation, the device (66) serves a simple authenticationpurpose, and an encrypted prerecorded reading of its expected magneticresponse is also incorporated into the 5 document. Conveniently in theexample given this could be incorporated into the bar code, or otherwisestored in a readable form. However, it will be appreciated that in moresophisticated systems it would be possible to store the expectedmagnetic signature remotely, optionally with further identificationand/or other security details.

The device in accordance with the invention applied to documentation inthis way serves primarily as a form of copy protection. It thereforeserves as a cheap and convenient authentication device in allcircumstances where there is a vulnerability to fraud arising from thecounterfeiting of genuine originals, for example in relation toidentification documents, formal certificates, financial paperwork suchas cheques, paper money and the like, important legal documents, andother such documentation.

Viewed from another aspect, there is provided a security device meanscomprising at least one magnetic element means, wherein said magneticelement means is responsive to an applied magnetic field to provide acharacteristic response.

Viewed from a further aspect, there is provided a method ofmanufacturing a security device, comprising the step of providing atleast one magnetic element, wherein said at least one magnetic elementprovides a characteristic response in response to an applied magneticfield.

Viewed from yet another aspect, there is provided a system for reading asecurity device means, comprising: a magnetic field generation means forapplying an applied magnetic field to a security device; and a detectionmeans for measuring one or more parameter representative of a measuredcharacteristic response of said security device in response to saidapplied magnetic field, wherein said system is operable to compare saidparameter(s) representative of a measured characteristic response to oneor more respective parameter(s) of a premeasured characteristic responseto determine whether respective of said parameters are substantiallyequivalent.

Viewed from another aspect, there is provided a method for reading asecurity device, comprising the step of applying an applied magneticfield to a security device; the step of measuring one or more parameterrepresentative of a measured characteristic response of said securitydevice in response to said applied magnetic field; and the step ofcomparing said parameter(s) representative of a measured characteristicresponse to one or more respective parameter(s) of a premeasuredcharacteristic response to determine whether respective of saidparameters are substantially equivalent.

Viewed from a further aspect, there is provided a product meanscomprising the security device means as herein described.

Those of ordinary skill in the art will realise that other techniquesmay be used to produce security devices. For example, instead ofproducing security devices using a lift off/wet etching process, ionbeam etching may be used. Those of ordinary skill in the art will alsobe aware that various embodiments of security devices can bemanufactured using various substrates, including, for example, silicon,glass, plastic, metals etc.

While certain of the example materials described herein areferromagnetic, those skilled in the art will realise that other types ofmagnetic and/or non-magnetic elements may be used provided they giverise to a suitable measurable characteristic response. For example,non-magnetic elements may be used where such elements produce ameasurable response in an applied magnetic field, where that responsecan be measured to provide a characteristic response.

Those of ordinary skill in the art will be aware of various techniquesthat can be used to manufacture and characterise magnetic elementssuitable for security devices. An example of one such manufacturingtechnique and one such characterisation process can be found in“Optimised process for the fabrication of mesoscopic magneticstructures,” Adeyeye et al, Journal of Applied Physics, Vol. 82, No. 1,pp. 469-473, 1 Jul. 1997, which investigated the effect of magneticelement size upon the magnetic properties thereof.

Embodiments produced in accordance with the invention may incorporatereflectivity/contrast enhancement measures either alone, or in anycombination. Materials such as gold, aluminium, chromium and/or tantalumcan be laid beneath and/or above magnetic elements to enhance theirreflectivity and/or the Kerr signal that the magnetic elements provide.Areas of a security device may be treated to reduce their reflectivityin order to improve the reflectivity/contrast between the magneticelements and their surrounding areas.

In various embodiments, magnetic elements in the shape of wires orflattened wires are provided. The end shape of such wires can becontrolled during manufacture of a security device. An angled end, forexample, from about 60° to about 90° may be provided. In various otherembodiments flattened ends and/or semi-circular ends may be provided toinfluence magnetic nucleation. The shape of the ends may be chosen toprovide improved magnetic switching characteristics.

Although the invention has been described in relation to particularembodiments, it will be appreciated that the invention is not limitedthereto, and that many variations are possible falling within the scopeof the invention.

It will be appreciated that certain of various embodiments of theinvention described above are implementable and/or configurable, atleast in part, using a data processing apparatus, such as, for example,hardware, firmware and/or a computer configured with a computer program.The computer program can be stored on a carrier medium in dataprocessing apparatus usable form. The carrier medium may be, forexample, solid-state memory, optical or magneto-optical memory such as areadable and/or writable disk for example a compact disk and a digitalversatile disk, or magnetic memory such as disc or tape, and the dataprocessing apparatus can utilise the program to configure it foroperation. The computer program may be supplied from a remote sourceembodied in a carrier medium such as an electronic signal, includingradio frequency carrier wave or optical carrier wave.

Those of ordinary skill in the art will be aware that the descriptionherein relates merely to illustrative examples of how the invention maybe put into effect, and that many embodiments incorporating one or morecomponents, e.g. of other embodiments, can be envisaged, along withfurther embodiments not explicitly described herein. For example, dataacquisition rates, sample rates, the number and size of samplequantisation levels, applied magnetic field cycling rates, the number ofaccumulated data sets, etc. may all be varied/selected as desired. Suchparameters may be varied programmably, for example, under the control ofa microprocessor, possibly in dependence upon various measuredconditions, such as, for example, temperature.

The scope of the present disclosure includes any novel feature orcombination of features disclosed herein either explicitly or implicitlyor any generalisation thereof irrespective of whether or not it relatesto the claimed invention or mitigates any or all of the problemsaddressed by the present invention. The applicant hereby gives noticethat new claims may be formulated to such features during theprosecution of this application or of any such further applicationderived therefrom. In particular, with reference to the appended claims,clauses, aspects and paragraphs, features from dependent claims,clauses, aspects and/or paragraphs may be combined with those of theindependent claims, clauses, aspects and/or paragraphs and features fromrespective independent claims, clauses, aspects and/or paragraphs may becombined in any appropriate manner and not merely in the specificcombinations enumerated.

1-64. (canceled)
 65. A security device comprising at least one magneticelement, wherein said at least one magnetic element is responsive to anapplied magnetic field to provide a characteristic response, whereinsaid at least one magnetic element is made from a material thatcomprises structural defects that cause brittle mode switching in whichthe growth of a single magnetic domain dominates the change inmagnetisation of a respective magnetic element.
 66. The security deviceof claim 65, wherein said at least one magnetic element is supported bya substrate.
 67. The security device of claim 66, wherein said at leastone magnetic element is supported on said substrate.
 68. The securitydevice of claim 65, wherein said at least one magnetic element isresponsive to said applied magnetic field to switch the magnetisation ormagnetic polarisation of said at least one magnetic element.
 69. Thesecurity device of claim 66, wherein said at least one magnetic elementis made from a magnetically soft material.
 70. The security device ofclaim 69, wherein said at least one magnetic element comprises amagnetically soft material selected from one or more of: nickel, iron,cobalt and alloys thereof with each other or silicon, such as nickeliron alloy, cobalt iron alloy, iron silicon alloy or cobalt siliconalloy.
 71. The security device of claim 69, wherein said magneticallysoft material is a permalloy material.
 72. The security device of claim65, wherein said at least one magnetic element is substantiallywire-shaped or flattened wire shaped.
 73. The security device of claim65, wherein said at least one magnetic element is backed by a lightreflective layer.
 74. The security device of claim 65, wherein said atleast one magnetic element is provided proximal a reduced lightreflectivity portion of said security device.
 75. The security device ofclaim 65, comprising a plurality of said at least one magnetic elements.76. The security device of claim 75, wherein said plurality of magneticelements is arranged to provide a linear pattern.
 77. The securitydevice of claim 75, wherein said plurality of magnetic elements isarranged to provide a two-dimensional pattern.
 78. The security deviceof claim 76, wherein said pattern encodes an identifier.
 79. Thesecurity device of claim 65, further comprising a unique identifierincorporated therewith.
 80. The security device of claim 79, whereinsaid unique identifier is provided by way of one or more of: anoptically readable bar code; one or more optical indicia; a magneticallyencoded identifier; and an electronic identifier.
 81. The securitydevice of claim 80, mounted upon a smart-card, wherein said electronicidentifier is provided by a smart-card chip provided on said smart-card.82. The security device of claim 65, wherein premeasured characteristicresponse information representing one or more measurable parameters ofsaid characteristic response is stored on said security device.
 83. Thesecurity device of claim 82, wherein said premeasured characteristicresponse information is in encrypted form.
 84. A method of manufacturinga security device, comprising: providing at least one magnetic elementcomprising structural defects, wherein said at least one magneticelement provides a brittle mode switching characteristic response inresponse to an applied magnetic field.
 85. The method of claim 84,comprising providing said at least one magnetic element on a substrate.86. The method of claim 84, comprising forming said at least onemagnetic element using a lift-off or wet etching process.
 87. The methodof claim 84, comprising forming said at least one magnetic element usingan ion beam etching process.
 88. The method of claim 84, comprisingmeasuring the magnitude(s) of one or more magnetic parameters of said atleast one magnetic element.
 89. The method of claim 88, comprisingmeasuring one or more of coercivity and jitter values.
 90. The method ofclaim 88, comprising using the measured magnitude(s) of said one or moremagnetic parameters to represent premeasured characteristic responseinformation.
 91. The method of claim 90, comprising encrypting saidpremeasured characteristic response information.
 92. The method of claim90, comprising storing said premeasured characteristic responseinformation in encrypted or unencrypted form on said security device.93. The method of claim 90, comprising storing said premeasuredcharacteristic response information in encrypted or unencrypted form ina storage medium remote from said security device.
 94. The method ofclaim 93, comprising storing said premeasured characteristic responseinformation in encrypted or unencrypted form in a database.
 95. Themethod of claim 84, further comprising providing said security devicewith a unique identifier.
 96. The method of claim 95 when dependant uponany one of claims 27 to 30, comprising storing a representation of saidunique identifier in association with said premeasured characteristicresponse information.
 97. A system for reading a security device,comprising: a magnetic field generation system for applying a magneticfield to a security device; and a detection system for measuring one ormore parameters representative of a brittle mode switching measuredcharacteristic response of said security device in response to saidmagnetic field, wherein said system is operable to compare said one ormore parameters representative of a brittle mode switching measuredcharacteristic response to one or more respective parameters of abrittle mode switching premeasured characteristic response to determinewhether respective measured and premeasured parameters are substantiallyequivalent.
 98. The system of claim 97, wherein the magnetic fieldgeneration system is operable to apply a time varying magnetic field toa security device.
 99. The system of claim 97, wherein a light beam isused to interrogate said security device.
 100. The system of claim 97,wherein said light beam is a visible or near-infrared beam produced by alaser diode.
 101. The system of claim 97, wherein said parametersrepresent one or more of coercivity and jitter values.
 102. The systemof claim 99, wherein said detection system incorporates magneto-opticKerr effect detection apparatus for detecting changes induced in saidlight beam by magnetic elements of said security device.
 103. The systemof claim 102, wherein said magneto-optic Kerr effect detection apparatusis configured to operate in transverse mode.
 104. The system of claim99, further operable to deflect said light beam across the surface ofsaid security device.
 105. The system of claim 99, further operable toread a unique identifier from said security device.
 106. The system ofclaim 105, wherein said unique identifier is identified by recognising apattern of magnetic elements supported by said security device.
 107. Thesystem of claim 105, wherein said unique identifier is identified byreading one or more of: an optically readable bar code; one or moreoptical indicia; a magnetically encoded identifier; and an electronicidentifier.
 108. The system of claim 97, further operable to determinesaid one or more respective parameters of the premeasured characteristicresponse by reading said one or more parameters from said securitydevice.
 109. The system of claim 97, further operable to determine saidone or more respective parameters of the premeasured characteristicresponse by reading said one or more parameters from a database. 110.The system of claim 109, wherein said database is remotely located fromsaid detection system.
 111. The system of claim 97, further operable todecrypt premeasured characteristic response information where it is reador provided in encrypted form.
 112. A method for reading a securitydevice, comprising: applying a magnetic field to a security device;measuring one or more parameters representative of a brittle modeswitching measured characteristic response of said security device inresponse to said magnetic field; and comparing said one or moreparameters representative of a brittle mode switching measuredcharacteristic response to one or more respective parameter(s) of abrittle mode switching premeasured characteristic response to determinewhether respective measured and premeasured parameters are substantiallyequivalent.
 113. The method of claim 112, comprising applying a timevarying magnetic field to a security device.
 114. The method of claim112, wherein measuring of one or more parameters representative of ameasured characteristic response of said security device in response tosaid magnetic field comprises measuring one or more of coercivity andjitter values.
 115. The method of claim 112, comprising interrogatingsaid security device using a light beam.
 116. The method of claim 112,comprising operating a laser to produce a visible or near-infrared beam.117. The method of claim 115, comprising detecting changes induced insaid light beam by magnetic elements of said security device using themagneto-optic Kerr effect.
 118. The method of claim 117, comprisingusing the magneto-optic Kerr effect transverse mode.
 119. The method ofclaim 115, comprising deflecting said light beam across the surface ofsaid security device.
 120. The method of claim 112, comprising reading aunique identifier from said security device.
 121. The method of claim120, comprising identifying said unique identifier by recognising apattern of magnetic elements supported by said security device.
 122. Themethod of claim 120, comprising identifying said unique identifier byreading one or more of; an optically readable bar code; one or moreoptical indicia; a magnetically encoded identifier; and an electronicidentifier.
 123. The method of claim 112, comprising determining saidrespective one or more parameters of the premeasured characteristicresponse by reading said one or more parameters from said securitydevice.
 124. The method of claim 112, comprising determining said one ormore respective parameters of the premeasured characteristic response byreading said one or more parameters from a database.
 125. The method ofclaim 124, comprising accessing a database remotely located from saiddetection system.
 126. The method of claim 112, further comprisingdecrypting premeasured characteristic response information where it isread or provided in encrypted form.
 127. A product comprising a securitydevice comprising at least one magnetic element, wherein said at leastone magnetic element is responsive to an applied magnetic field toprovide a characteristic response, wherein said at least one magneticelement is made from a material that comprises structural defects thatcause brittle mode switching in which the growth of a single magneticdomain dominates the change in magnetisation of a respective magneticelement.
 128. The product of claim 127, comprising one or more of: adocument; a passport; an identity card; a compact disc; a digitalversatile disc; a software product; packaging; an item of clothing; anitem of footwear; a smart-card; a credit or bank card; a cosmetic item;an engineering part; an accessory; and any other goods and/or items ofcommerce, whether manufactured or otherwise.